1. Field of the Invention
The present invention relates generally to solar concentrators, and more particularly to a wide angle, self tracking solar concentrator.
2. Description of the Related Art
Solar concentrators collect sunlight over some area and direct the sunlight onto a (photovoltaic) solar cell of much smaller area. In this way, the optical power incident on a relatively large area is collected and converted to electrical power, at some efficiency, by a relatively small solar cell. The solar cell is typically based on crystalline silicon or gallium-arsenide. One reason for employing a concentrator is that solar cells are currently the most expensive component of photovoltaic arrays on a per unit area basis. Another reason is that photovoltaic materials are more efficient at higher power levels than that of ordinary sunlight.
Typical prior art solar concentrators employ a Fresnel lens to focus incident sunlight onto the solar cell. If the Fresnel lens and solar cell are stationary as the sun moves overhead, the focal spot will move across and eventually off of the small solar cell. In other words, the field of view of the optical system is very limited. In order to compensate for this limitation, concentrator systems are typically designed to track the sun, i.e. the optic axis of the system is continuously or periodically mechanically adjusted to be directed at the sun throughout the day and year. However, such periodical mechanical adjustments require a relatively complex, costly structure. In addition, power is required to make the adjustments, thereby reducing the overall efficiency of the system.
The present invention is directed to a self tracking solar concentration which employs at least one collector lens to at least partially focus incident sunlight onto at least one array of lens elements, such as, for example, a Fresnel lens array. Each element of the lens array is preferably smaller than the collector lens. As the sun moves overhead, the partially focused sunlight moves across each element of the lens array. For a particular angular position of the sun, a respective element of the lens array focuses the incident sunlight onto one edge of the solar cell. As the angular position of the sun changes, the focal spot moves across the surface of the solar cell and eventually off the opposite edge of the cell. As this occurs the partially focused beam moves across the element of the lens array and onto an adjacent element. This latter element of the lens array keeps the final focal spot on the surface of the solar cell for a contiguous range of angular motion of the sun. Thus, the solar concentrator described herein effectively tracks the sun without requiring mechanical motion of the system and provides a significantly broader field of view than conventional solar concentrators. This broad field of view advantageously directs sunlight which is scattered or diffused before reaching the surface of the solar panel onto the solar cell. In the most direct implementations of the present invention, the field of view of the system is effectively divided into angular sectors each one of which employs one element of the lens array to keep the focused radiation on the surface of a solar cell for a range of angles. Ordinarily the system will be designed so that these angular ranges are contiguous in order to maximize the collection of both direct, scattered, and diffused sunlight.
In alternative embodiments, an array of collector lenses, an array of lens arrays and/or an array of solar cells is employed in the solar concentrator described herein.